The guy was facing an armed robber who was implicitly threatening to shoot and kill innocent people. It is not unusual for this type of criminal to kill his victims after robbing them. It is common for firearms instructors to teach that when in self defense situation in fear of your life, keep shooting until the perp is down or you run out of ammo. It's amazing how many shots a bad guy can absorb and still shoot back and kill you.
It’s also not unusual that he has an accomplice right outside the door a nanosecond from charging in. It’s a large leap of faith people make when they assume the action is over when bad guy 1 was on the floor. And he could have had a hand starting to move for another gun.
This guy did good. But it scares effete Easterners and prigs.